All options can be abbreviated to their shortest unique prefix. You
may use two hyphens instead of one to designate an option. You may
use either white space or equals signs between an option name and its
value.

DESCRIPTION This program is part of Netpbm.

pnmshear reads a PNM image as input and shears it by the specified
angle and produce a PNM image as output. If the input file is in
color, the output will be too, otherwise it will be grayscale. The
angle is in degrees (floating point), and measures this:

The angle should not get too close to 90 or -90, or the resulting
image will be unreasonably wide.

pnmshear does the shearing by looping over the source pixels and dis-
tributing fractions to each of the destination pixels. This has an
'anti-aliasing' effect - it avoids jagged edges and similar artifacts.
However, it also means that the original colors in the image are modi-
fied and there are typically more of them than you started with. If
you need to keep precisely the same set of colors, see the -noan-tialias option. If the expanded palette is a problem, you can run the
result through pnmquant.